This one (so others can find it easier): Dual Boot Problems with Windows and Manjaro
Out of the 100+ posts there, I do not think we ever got the proper output of:
lsblk -f
When you did before, it did out output properly.
But I believe you have Manjaro installed on:
nvme1n1
├─nvme1n1p1 ext4 1.0 7577eecb-23f7-4a07-8eac-a01a3d8d9240 1,3T 21% /
└─nvme1n1p2 swap 1 swap 8708d9e9-4e5b-490b-b93e-465abbd4a30a [SWAP]
(And it definitely boots MBR/Legacy.)
@Umbra_noctis with the update, did you install the pacnew for /etc/mkinitcpio.conf, then it would not boot?
Since you had trouble with configuration files, I think this a stretch to say you merged that file.
With manjaro-chroot try it without -a, but mount your root first.
Example:
sudo mount /dev/nvme1n1p1 /mnt
sudo manjaro-chroot /mnt /bin/bash
If that doesn’t work, you will have to do it the Arch Linux way. (Just more mount commands.)